We propose the development of an instrument to measure the concentration of nitric oxide(NO) in exhaled breath as an asthma diagnosis tool. The analyzer uses the combination of a proprietary hollow optical waveguide measurement cell, tunable semiconductor laser, and wavelength modulation spectroscopy to provide sensitive and reliable measurements of NO in air. The sensor will exhibit rapid response time (<1 s), low minimum detection limits (100's of parts per trillion for NO in air) and will be physically compact relative to other sensors with similar sensitivity. The compact, lightweight nature of the sensor coupled with its sensitivity provides a significant innovation in comparison to existing technologies. In Phase I, a benchtop measurement system will be constructed and tested. The system will be challenged with a variety of concentrations of NO in laboratory air. Phase II will consist of the development and optimization of a prototype instrument that will be used in research trials with human subjects. The gas sensor will be interfaced to a pneumatic sampling system that will allow exhaled breath samples to be tested. Once the system is functioning a small sample of human subjects will be tested in collaboration with Aerocrine AB, a commercial biomedical device company. PROPOSED COMMERCIAL APPLICATIONS: The proposed device would have applications in hospitals, emergency rooms, and doctors' offices and perhaps even in home use in monitoring of NO in exhaled breath as a tool for asthma diagnosis and control. Other applications are possible in the diagnosis of sick bowel syndrome, urinary tract infection and exhaled breath analysis for CO in cystic fibrosis patients. Finally the development of this technology has far reaching applications in indoor health and environmental monitoring.